Regulation of contraction of microfilament rings will be studied during embryonic development of a mollusk. Polar lobes are cytoplasmic protuberances which form and resorb on the fertilized eggs of the marine mudsnail, Ilyanassa obsoleta (Nassarius obsoletus), by constriction and relaxation of a microfilament ring. As in cytokinesis, ring constriction appears to be regulated by microtubules and calcium ions. We will isolate antibodies to highly purified proteins from muscle and non-muscle cells, label such antibodies, and use them to localize at the ultrastructural level the structural and regulatory proteins of the microfilament ring of the polar lobe constriction. We will use atomic absorption spectroscopy, isotopes, and ion-selective microelectrodes to determine the intracellular ionic conditions controlling the activity of microfilament rings. Potential regulatory molecules or antibodies to them will be labeled and injected directly into eggs by microiontophoresis or pressure in order to alter microfilament function. Binding sites of injected substances, as well as normal endogenous sites of calcium sequestration, will be determined by electron microscopy.